Display all favorited pics on the user's profile page.
Add favorite button to posts shown in index page.
Add to the post index page so that favorite links are only shown if user is signed in. Unfavorite links are shown for posts they have favorited, and favorite links are shown for the rest. Add links to the profile page to see all posts as well as a link to see all the user's posts. Add a link to see all posts to the home page.
Make home page display favorite button only if logged in, and only if not favorited yet. If it has been favorited by the current user, the Un-Favorite button is shown.: